ABSTRACT
When similar stimuli are mapped onto different responses in speeded classification tasks (A → R +; a → R -), response performance is usually impaired as compared to appropriate control conditions with dissimilar stimuli (B → R +; c → R -). A framework for the analysis of the effect is presented. The impairment is assumed to reflect an increase in response competition that arises from the similarity of the stimuli. The increase can be avoided if the subject bases his response decisions on internal representations which do not contain those attributes which are shared by the competing alternatives. The selective reduction of the attributes can pertain either to the internal representations which are automatically activated by the stimulus information (set of stimulus-induced attributes) or to the representations of the response criteria which are constructed on the basis of the information in the instructions (sets of response-defining attributes). It is argued that these two modes of selective reduction can be separated from each other under bias conditions. Illustrative data suggest the conclusion that the structure of the attribute lists (selectivity) depends on stimulus bias whereas their dynamical state (readiness) is controlled by response bias.
